With the increasing use of word-processing and data-processing apparatus utilizing computer technology, there has been a widely-recognized desire far greater amounts of data storage per unit of storage media, and this has brought about the need for advancements in the associated technology to achieve ever-greater, bit-packing densities as well as greater track densities. One achievement resulting from this requirement has been the development and use of embedded servo techniques, in which closely-spaced recording tracks on the media are predefined by positioning information recorded on the storage media prior to its use for actual data storage operations, by which closed-loop servo-positioning may be used to follow the pre-recorded tracks. While there have been different proposals for different embedded servo information formats, one particular such format viewed as having a number of advantages, particularly when used with magnetic tape media (with respect to which few developments have as yet been realized) is disclosed and claimed in previously-filed and copending U.S. Pat. application Ser. No. 280,138, now U.S. Pat. No. 472,750, assigned to the assignor of the present invention. The disclosure in that application is to be deemed incorporated herein by reference.
Typically in the use of embedded servo techniques, the head-positioning information is pre-recorded on the media by the manufacturer of the storage device, i.e., the disc drive or tape drive. This is virtually an essential requirement, since it goes without saying that if the recording tracks are to be so densely packed as to require closed-loop servoing techniques in order to keep transducer head in alignment with a selected track for data-recording or data-reading purposes, one would not anticipate that the storage device would be able to locate and follow the desired location for each such track prior to the time the positioning information has been recorded on the storage media. Thus, the servo-writing process, by which the head-positioning information is pre-recorded on the storage media to define the closely-packed recording tracks, has generally been considered as requiring specialized and expensive apparatus, available only at the manufacturer. For example, the servo-writing apparatus heretofore used has had to embody very accurately controlled recording-media transport capabilities, so that there will be virtually no speed variation along each different track. Further, the path of movement followed by the recording media in transport must be very accurately controlled with respect to the recording head, or transducer, to guard against the inherent variations and non-linearities in mechanical transport systems. A similar factor is the need for a very high degree of stability in the support structure for both the media and the drive itself. Considering the exceedingly narrow widths and closely-packed relationship of the various recording tracks to be defined on the media, this requirement has involved the use of massive support tables and footings for the servo-writing apparatus.
The resultant high cost of servo-writing units has essentially mandated that only the manufacturers of the media or of the storage devices (drives) have such equipment, and this in turn has meant that the pre-recorded media was available only from such manufacturers even though the media itself, absent the pre-recorded positioning information, is available from many sources. This has imposed added expense and added inconvenience for the end user, particularly in instances when the pre-recorded media is in short supply or temporarily unavailable.